Partial Effect: Solution was more clear but the phase-separated layer remained. Water additions were tested in 0.01% increments.

Seafoam

No increase in water holding.

Valvoline - Nitro Shot

No increase in water holding.

Nov. 21, 2014

Ethanol will mix with water, which means gasoline-ethanol blends can hold water. This is of particular concern for small engines and engines that are used intermittently because they can become contaminated from condensation or rainfall during storage. Water in fuel can cause multiple problems, including:

Water can cause an engine not to start. In tests by Gregory Davis at Kettering University small engines failed to start when water was introduced at levels greater than 20 teaspoons per gallon. In the study high levels of water contamination were equally bad for pure gasoline and ethanol blends.

Water contamination during storage can lead to the formation of acid compounds that can damage fuel system components.

A number of off-the-shelf fuel additives purport to help hold water in solution, so we wanted to look at this more closely to answer two questions:

How much water can E10 and E15 gasoline ethanol blends hold in solution?

Can off-the-shelf fuel additives increase the amount of water held in solution?

Conclusions

Unlike pure gasoline, ethanol blends can hold small amounts of water in solution which is then run through the engine harmlessly. In pure gasoline small amounts of water can build up in the tank.

Only two of fuel additives tested increased the amount of water held in solution. All claimed on their label to "remove water," "solve phase separation," "dry the fuel," etc.

Recommendations

Use fresh fuel, preferably within 30 days of purchase.

Store lawn mower and other small engines empty in a dry place. (If the fuel tank is not empty, store it completely full to minimize air space.) Fuel additives for fuel stabilization are recommended by many manufacturers. This study did not test these other additive properties.

A large amount of water contamination in a fuel tank is likely equally bad for E-0 or an ethanol blend. Avoid water contamination by covering small engines or storing them in a shed or garage.